Add drupalGet() to KernelTestBase

Made a very rough start on a branch.

1. Huge +1. Love this idea.
2. It'd be great to be able to use this to check the output from a View page display, too.

Thanks!
-Derek

Got it working!

The methods in BrowserHtmlDebugTrait aren't going to work for kernel tests -- they occasionally make assumptions about having Mink. So my approach has been to make a parallel KernelHtmlDebugTrait. It deviates very little, so as a follow-up we should look at merging them. Things to change include:

- make the $message param of htmlOutput() required, not optional. There's only one place that htmlOutput() is called without it
- changing how getHtmlOutputHeaders() works
- fixing how $this->htmlOutputTestId is obtained
- ... other things I may have forgotten about.

Linking the original issue

Rather than adding one method, writing a kernel based mink driver would be ideal

Copying from slack

https://github.com/symfony/symfony/blob/6.4/src/Symfony/Bundle/Framework...

Looks like symfony have a solution for this that uses sub processes

If we can get this to work we get drupalGet, submitForm, assertSession etc all for free

That was the original intent of step 3